Loss of GABA-mediated inhibition in the spinal cord is proposed to contribute to the development and maintenance of neuropathic pain. However, the supporting data are surprisingly weak. Further, these studies have not considered the complex molecular biology of GABA receptors, and how subunit composition and pharmacology change in disease states and under conditions of repetitive activity as occurs after nerve injury. We hypothesize that nerve injury causes immediate, as well as long-term changes in the expression, distribution and subunit composition of GABAA or GABAB receptors in the spinal cord. We propose to characterize these changes in the context of defined presynaptic and postsynaptic elements of the afferent pain pathways and a well-characterized model of spinal nerve ligation that exhibits time-dependent changes in neuropathic pain behaviors. Of particular importance are the changes induced in the expression and molecular composition of these receptors on uninjured, and on injured primary afferent neurons and on dorsal horn neurons as a function of time after nerve injury. Changes in the expression and subunit composition of GABAA and GABAB receptor subunits in the spinal cord dorsal horn, and in ipsilateral and contralateral L4 and L5 DRG of ligated and sham rats will be determined by Western blot. Two-color indirect immunofluorescence methods will be used with stereological measurements to examine the distribution of GABAA and GABAB receptor subunits on different populations of immunohistochemically-identified primary afferent neurons in the L4 and L5 DRG of ligated and sham-operated rats. Immunohistochemical methods will also be used in conjunction with retrograde labeling of spinothalamic and spinoparabrachial neurons in ligated and sham rats to determine whether the distribution and composition of postsynaptic GABAA and GABAB receptors in the spinal cord dorsal horn is also altered after nerve injury. Time points for analysis will range 7 to 140 days after injury. These studies will provide new information about the distribution of GABAA and GABAB receptors on identified populations of primary afferent neurons and dorsal horn neurons in the naive animal. They will describe how the distribution and molecular composition of these receptors changes as a function of time after nerve injury and provide new insights into the molecular and neuroanatomical bases of inhibitorv svnaptic transmission in the spinal cord.